DOES SILICONE GASKET MATERIAL DESTROY ENGINES?

2006 Citroen Picasso • 71,000 miles

I purchased a replacement 1.6HDi Citroen Xzara Picasso engine. A mobile mechanic transferred all the ancillary parts from the previous engine onto it and fitted it to the vehicle. After less than 500 miles (having run it gently to 'run it in') the noise of big end/main bearings suddenly occured. The engine was extracted and sent back to Direct Engines UK Ltd (the supplier) with the turbo, cooling and fuel system in place for their inspection. They are now claiming that the cause of this catostrophic failure is silicone gasket particles used by my mechanic, blocking the oilways that supply underside of the pistons and the crank bearings. They said silicone should never ever be used on these engines but my mechanic (who admits to having used some silicone on this engine) claims he has used silicone to bolster rubber gaskets etc for the last 30 years with no problem. Are the engine company simply trying to avoid blame for a poorly assembled engine?

Hard to say without seeing it, but it is indeed common to use silicone gasket sealers with and without rubber gaskets. A rebuilt engine typically is supplied with all parts installed already that can let sealer get into the oil. Mainly that's valve covers and the oil pan. The only thing that was an issue a few years ago was that some formulations of sealants gave off fumes that destroyed oxygen sensors. Most tubes of sealers have "oxygen sensor safe" printed on them now.

Even if a chunk of gasket material broke off, it would have been sucked up by the oil pump and trapped in the filter. It should not have gotten to the bearings. A more common source of the type of failure you mentioned is incomplete cleaning of oil passages and the rest of the block after any machining procedures that create metal chips. Sooner or later that happens to all of us and we simply have to do the job over. That's what warranties are for.

Thanks for that.
I asked them te question about why the oil filter had not picked it up and they claim it's because the sealant was on the oil filter housing to block (the other side of the filter). Would it really be able to stick in an oilway against the oil pressure and then starve the crank of oil? Isn't the crank and its bearings partially bathed in oil from the sump anyway? They are saying the bearing shells are totally dry and down to the copper! Is that possible from a few pieces of silicone? Seems a bit far fetched to me and I feel they are just trying to discredit my mechanic to avoid any blame.

Nope. If that's true, they could be correct, but that housing is normally attached by the engine builder, not the person installing the engine. You typically wouldn't need sealant on that gasket, but even if you did put some there, that stuff skins over in about 20 minutes. If your mechanic bolted that housing on with sealant before installing the engine into the car, it would have had hours to set up, and it's not going to break off and plug anything after that. Even if I could see those bearings myself, it would likely be almost impossible to say who to believe. If there was sealant in the holes in the crankshaft that feed the oil to the bearings, then it would likely be the mechanic's fault. Rebuilders don't run the engine so even if they used the sealant, it would be cured by the time they shipped the engine to you. It's not going to go anywhere after that.

It's also possible WAY too much sealant was used. Some inexperienced mechanics glop everything full in hopes it will squish into places they might otherwise overlook. That could easily plug a passage to or from the oil filter, but then there wouldn't be any pressure at the sending unit and your warning light would have been on.

Either way, it's hard to imagine how the bearings could have lasted for 500 miles without oil. The crank doesn't sit in the oil. In fact, that would cause more problems. The oil sits low enough in the pan to be kept away from the spinning crankshaft and its counterweights. Many engines even use a "windage tray" just under the crankshaft. That is to prevent the wind from the spinning crankshaft from whipping up the oil and aerating it. Air bubbles in the oil compress and reduce its ability to isolate moving parts from each other, namely the crankshaft and connecting rod bearings.

I don't know about your specific engine, but most engines send oil to the camshaft bearings through the crankshaft bearings, so if the passages were blocked enough to destroy the main, (crankshaft) bearings, the connecting rod and camshaft bearings should show similar wear. Hydraulic lifters, when used, typically sit in their own oil passages that aren't fed from the main bearings so they would pump up normally. If they were noisy, that would indicate the oil passage was blocked closer to the filter.

If this engine came from a high-volume rebuilder, they have everything down to a science and they know what to do to avoid problems. For that reason, I'm inclined to agree that the mechanic's use of gasket sealer caused the problem. Still, you have no way of knowing if something got overlooked when they built the engine.

I have an engine that was rebuilt by my students a few years ago. It failed after 40 miles. New crankshaft and bearings and it's been fine for over 600 miles. We never did find the cause of the original failure.

Thank you. I'm stuck at the moment as to what to do. I live in Birmingham UK and the engine with my ancillaries on is 500 miles away in Scotland. They (direct engines UK, who incidentally have given extremely poor customer service) are accusing my mechanic of silicone contamination and my mechanic is accusing them of poor rebuild (swarf etc). Neither wants to accept liability. Meanwhile it's me that's sitting here with a car with no engine! I've got a terrible feeling that I'm going to be the one who has to pay the 550 they want for the new crank and bearings! Think I may need to seek an indepenent inspection and/or legal assistance. Paul.

I just repaired an engine that someone had re built with heaps of silicone sealant, so much that it extruded into the engine and was picked up in the oil and blocked the strainer, this engine was basically destroyed due to lack of oil pressure a direct resault of improper use of silicon sealant.

Thanks for that. There was definitely no oil pressure warning/issue. My mechanic has 30 years experience and regularly uses silicone. Looking on line, silicone use seems to be an acceptable practice as long as it's a smear and not a shovel full. If you were to listen to the engine supplier though, they would have you believe it is the ultimate sin!
The engine was running perfectly one minute and sudden bottom end knocking the next. Just don't know how to constructively progress this if no one will accept liability?
Paul.

I wouldn't want to be stuck in the middle either. Perhaps you could mediate a compromise. Offer to pay for the parts if the rebuilder will cover the labor and shipping. That will give them an "out" without admitting fault, and will let them at least give the appearance of being concerned with customer satisfaction.

Part of the labor you pay a shop goes to cover work they have to do over again but can't charge you for. That includes replacing defective new parts, parts damaged by the mechanic, and work done improperly the first time. You can expect to pay a second time for work you did yourself that led to a problem, but that doesn't apply in this case.

Ask the mechanic if he will install the replacement engine at no charge. Even half the normal charge might be an acceptable compromise. To be safe, request he not use any silicone sealer, at least at first. In the somewhat unlikely event a leak develops, let him handle that at a later time once the reliability of the new engine has been proven.